# SPDX-License-Identifier: GPL-2.0-only
config DEFCONFIG_LIST
string
depends on !UML
option defconfig_list
default "/lib/modules/$(shell,uname -r)/.config"
default "/etc/kernel-config"
default "/boot/config-$(shell,uname -r)"
default ARCH_DEFCONFIG
default "arch/$(ARCH)/defconfig"
config CC_IS_GCC
def_bool $(success,$(CC) --version | head -n 1 | grep -q gcc)
config GCC_VERSION
int
default $(shell,$(srctree)/scripts/gcc-version.sh $(CC)) if CC_IS_GCC
default 0
config CC_IS_CLANG
def_bool $(success,$(CC) --version | head -n 1 | grep -q clang)
config CLANG_VERSION
int
default $(shell,$(srctree)/scripts/clang-version.sh $(CC))
config CC_CAN_LINK
def_bool $(success,$(srctree)/scripts/cc-can-link.sh $(CC))
config CC_HAS_ASM_GOTO
def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))
config TOOLS_SUPPORT_RELR
def_bool $(success,env "CC=$(CC)" "LD=$(LD)" "NM=$(NM)" "OBJCOPY=$(OBJCOPY)" $(srctree)/scripts/tools-support-relr.sh)
config CC_HAS_ASM_INLINE
def_bool $(success,echo 'void foo(void) { asm inline (""); }' | $(CC) -x c - -c -o /dev/null)
config CC_HAS_WARN_MAYBE_UNINITIALIZED
def_bool $(cc-option,-Wmaybe-uninitialized)
help
GCC >= 4.7 supports this option.
config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
bool
depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9
help
GCC's -Wmaybe-uninitialized is not reliable by definition.
Lots of false positive warnings are produced in some cases.
If this option is enabled, -Wno-maybe-uninitialzed is passed
to the compiler to suppress maybe-uninitialized warnings.
config CONSTRUCTORS
bool
config IRQ_WORK
bool
config BUILDTIME_EXTABLE_SORT
bool
config THREAD_INFO_IN_TASK
bool
help
Select this to move thread_info off the stack into task_struct. To
make this work, an arch will need to remove all thread_info fields
except flags and fix any runtime bugs.
One subtle change that will be needed is to use try_get_task_stack()
and put_task_stack() in save_thread_stack_tsk() and get_wchan().
menu "General setup"
config BROKEN
bool
config BROKEN_ON_SMP
bool
depends on BROKEN || !SMP
default y
config INIT_ENV_ARG_LIMIT
int
default 32 if !UML
default 128 if UML
help
Maximum of each of the number of arguments and environment
variables passed to init from the kernel command line.
config COMPILE_TEST
bool "Compile also drivers which will not load"
depends on !UML
default n
help
Some drivers can be compiled on a different platform than they are
intended to be run on. Despite they cannot be loaded there (or even
when they load they cannot be used due to missing HW support),
developers still, opposing to distributors, might want to build such
drivers to compile-test them.
If you are a developer and want to build everything available, say Y
here. If you are a user/distributor, say N here to exclude useless
drivers to be distributed.
config HEADER_TEST
bool "Compile test headers that should be standalone compilable"
help
Compile test headers listed in header-test-y target to ensure they are
self-contained, i.e. compilable as standalone units.
If you are a developer or tester and want to ensure the requested
headers are self-contained, say Y here. Otherwise, choose N.
config KERNEL_HEADER_TEST
bool "Compile test kernel headers"
depends on HEADER_TEST
help
Headers in include/ are used to build external moduls.
Compile test them to ensure they are self-contained, i.e.
compilable as standalone units.
If you are a developer or tester and want to ensure the headers
in include/ are self-contained, say Y here. Otherwise, choose N.
config UAPI_HEADER_TEST
bool "Compile test UAPI headers"
depends on HEADER_TEST && HEADERS_INSTALL && CC_CAN_LINK
help
Compile test headers exported to user-space to ensure they are
self-contained, i.e. compilable as standalone units.
If you are a developer or tester and want to ensure the exported
headers are self-contained, say Y here. Otherwise, choose N.
config LOCALVERSION
string "Local version - append to kernel release"
help
Append an extra string to the end of your kernel version.
This will show up when you type uname, for example.
The string you set here will be appended after the contents of
any files with a filename matching localversion* in your
object and source tree, in that order. Your total string can
be a maximum of 64 characters.
config LOCALVERSION_AUTO
bool "Automatically append version information to the version string"
default y
depends on !COMPILE_TEST
help
This will try to automatically determine if the current tree is a
release tree by looking for git tags that belong to the current
top of tree revision.
A string of the format -gxxxxxxxx will be added to the localversion
if a git-based tree is found. The string generated by this will be
appended after any matching localversion* files, and after the value
set in CONFIG_LOCALVERSION.
(The actual string used here is the first eight characters produced
by running the command:
$ git rev-parse --verify HEAD
which is done within the script "scripts/setlocalversion".)
config BUILD_SALT
string "Build ID Salt"
default ""
help
The build ID is used to link binaries and their debug info. Setting
this option will use the value in the calculation of the build id.
This is mostly useful for distributions which want to ensure the
build is unique between builds. It's safe to leave the default.
config HAVE_KERNEL_GZIP
bool
config HAVE_KERNEL_BZIP2
bool
config HAVE_KERNEL_LZMA
bool
config HAVE_KERNEL_XZ
bool
config HAVE_KERNEL_LZO
bool
config HAVE_KERNEL_LZ4
bool
config HAVE_KERNEL_UNCOMPRESSED
bool
choice
prompt "Kernel compression mode"
default KERNEL_GZIP
depends on HAVE_KERNEL_GZIP || HAVE_KERNEL_BZIP2 || HAVE_KERNEL_LZMA || HAVE_KERNEL_XZ || HAVE_KERNEL_LZO || HAVE_KERNEL_LZ4 || HAVE_KERNEL_UNCOMPRESSED
help
The linux kernel is a kind of self-extracting executable.
Several compression algorithms are available, which differ
in efficiency, compression and decompression speed.
Compression speed is only relevant when building a kernel.
Decompression speed is relevant at each boot.
If you have any problems with bzip2 or lzma compressed
kernels, mail me (Alain Knaff) . (An older
version of this functionality (bzip2 only), for 2.4, was
supplied by Christian Ludwig)
High compression options are mostly useful for users, who
are low on disk space (embedded systems), but for whom ram
size matters less.
If in doubt, select 'gzip'
config KERNEL_GZIP
bool "Gzip"
depends on HAVE_KERNEL_GZIP
help
The old and tried gzip compression. It provides a good balance
between compression ratio and decompression speed.
config KERNEL_BZIP2
bool "Bzip2"
depends on HAVE_KERNEL_BZIP2
help
Its compression ratio and speed is intermediate.
Decompression speed is slowest among the choices. The kernel
size is about 10% smaller with bzip2, in comparison to gzip.
Bzip2 uses a large amount of memory. For modern kernels you
will need at least 8MB RAM or more for booting.
config KERNEL_LZMA
bool "LZMA"
depends on HAVE_KERNEL_LZMA
help
This compression algorithm's ratio is best. Decompression speed
is between gzip and bzip2. Compression is slowest.
The kernel size is about 33% smaller with LZMA in comparison to gzip.
config KERNEL_XZ
bool "XZ"
depends on HAVE_KERNEL_XZ
help
XZ uses the LZMA2 algorithm and instruction set specific
BCJ filters which can improve compression ratio of executable
code. The size of the kernel is about 30% smaller with XZ in
comparison to gzip. On architectures for which there is a BCJ
filter (i386, x86_64, ARM, IA-64, PowerPC, and SPARC), XZ
will create a few percent smaller kernel than plain LZMA.
The speed is about the same as with LZMA: The decompression
speed of XZ is better than that of bzip2 but worse than gzip
and LZO. Compression is slow.
config KERNEL_LZO
bool "LZO"
depends on HAVE_KERNEL_LZO
help
Its compression ratio is the poorest among the choices. The kernel
size is about 10% bigger than gzip; however its speed
(both compression and decompression) is the fastest.
config KERNEL_LZ4
bool "LZ4"
depends on HAVE_KERNEL_LZ4
help
LZ4 is an LZ77-type compressor with a fixed, byte-oriented encoding.
A preliminary version of LZ4 de/compression tool is available at
.
Its compression ratio is worse than LZO. The size of the kernel
is about 8% bigger than LZO. But the decompression speed is
faster than LZO.
config KERNEL_UNCOMPRESSED
bool "None"
depends on HAVE_KERNEL_UNCOMPRESSED
help
Produce uncompressed kernel image. This option is usually not what
you want. It is useful for debugging the kernel in slow simulation
environments, where decompressing and moving the kernel is awfully
slow. This option allows early boot code to skip the decompressor
and jump right at uncompressed kernel image.
endchoice
config DEFAULT_HOSTNAME
string "Default hostname"
default "(none)"
help
This option determines the default system hostname before userspace
calls sethostname(2). The kernel traditionally uses "(none)" here,
but you may wish to use a different default here to make a minimal
system more usable with less configuration.
#
# For some reason microblaze and nios2 hard code SWAP=n. Hopefully we can
# add proper SWAP support to them, in which case this can be remove.
#
config ARCH_NO_SWAP
bool
config SWAP
bool "Support for paging of anonymous memory (swap)"
depends on MMU && BLOCK && !ARCH_NO_SWAP
default y
help
This option allows you to choose whether you want to have support
for so called swap devices or swap files in your kernel that are
used to provide more virtual memory than the actual RAM present
in your computer. If unsure say Y.
config SYSVIPC
bool "System V IPC"
---help---
Inter Process Communication is a suite of library functions and
system calls which let processes (running programs) synchronize and
exchange information. It is generally considered to be a good thing,
and some programs won't run unless you say Y here. In particular, if
you want to run the DOS emulator dosemu under Linux (read the
DOSEMU-HOWTO, available from ),
you'll need to say Y here.
You can find documentation about IPC with "info ipc" and also in
section 6.4 of the Linux Programmer's Guide, available from
.
config SYSVIPC_SYSCTL
bool
depends on SYSVIPC
depends on SYSCTL
default y
config POSIX_MQUEUE
bool "POSIX Message Queues"
depends on NET
---help---
POSIX variant of message queues is a part of IPC. In POSIX message
queues every message has a priority which decides about succession
of receiving it by a process. If you want to compile and run
programs written e.g. for Solaris with use of its POSIX message
queues (functions mq_*) say Y here.
POSIX message queues are visible as a filesystem called 'mqueue'
and can be mounted somewhere if you want to do filesystem
operations on message queues.
If unsure, say Y.
config POSIX_MQUEUE_SYSCTL
bool
depends on POSIX_MQUEUE
depends on SYSCTL
default y
config CROSS_MEMORY_ATTACH
bool "Enable process_vm_readv/writev syscalls"
depends on MMU
default y
help
Enabling this option adds the system calls process_vm_readv and
process_vm_writev which allow a process with the correct privileges
to directly read from or write to another process' address space.
See the man page for more details.
config USELIB
bool "uselib syscall"
def_bool ALPHA || M68K || SPARC || X86_32 || IA32_EMULATION
help
This option enables the uselib syscall, a system call used in the
dynamic linker from libc5 and earlier. glibc does not use this
system call. If you intend to run programs built on libc5 or
earlier, you may need to enable this syscall. Current systems
running glibc can safely disable this.
config AUDIT
bool "Auditing support"
depends on NET
help
Enable auditing infrastructure that can be used with another
kernel subsystem, such as SELinux (which requires this for
logging of avc messages output). System call auditing is included
on architectures which support it.
config HAVE_ARCH_AUDITSYSCALL
bool
config AUDITSYSCALL
def_bool y
depends on AUDIT && HAVE_ARCH_AUDITSYSCALL
select FSNOTIFY
source "kernel/irq/Kconfig"
source "kernel/time/Kconfig"
source "kernel/Kconfig.preempt"
menu "CPU/Task time and stats accounting"
config VIRT_CPU_ACCOUNTING
bool
choice
prompt "Cputime accounting"
default TICK_CPU_ACCOUNTING if !PPC64
default VIRT_CPU_ACCOUNTING_NATIVE if PPC64
# Kind of a stub config for the pure tick based cputime accounting
config TICK_CPU_ACCOUNTING
bool "Simple tick based cputime accounting"
depends on !S390 && !NO_HZ_FULL
help
This is the basic tick based cputime accounting that maintains
statistics about user, system and idle time spent on per jiffies
granularity.
If unsure, say Y.
config VIRT_CPU_ACCOUNTING_NATIVE
bool "Deterministic task and CPU time accounting"
depends on HAVE_VIRT_CPU_ACCOUNTING && !NO_HZ_FULL
select VIRT_CPU_ACCOUNTING
help
Select this option to enable more accurate task and CPU time
accounting. This is done by reading a CPU counter on each
kernel entry and exit and on transitions within the kernel
between system, softirq and hardirq state, so there is a
small performance impact. In the case of s390 or IBM POWER > 5,
this also enables accounting of stolen time on logically-partitioned
systems.
config VIRT_CPU_ACCOUNTING_GEN
bool "Full dynticks CPU time accounting"
depends on HAVE_CONTEXT_TRACKING
depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
depends on GENERIC_CLOCKEVENTS
select VIRT_CPU_ACCOUNTING
select CONTEXT_TRACKING
help
Select this option to enable task and CPU time accounting on full
dynticks systems. This accounting is implemented by watching every
kernel-user boundaries using the context tracking subsystem.
The accounting is thus performed at the expense of some significant
overhead.
For now this is only useful if you are working on the full
dynticks subsystem development.
If unsure, say N.
endchoice
config IRQ_TIME_ACCOUNTING
bool "Fine granularity task level IRQ time accounting"
depends on HAVE_IRQ_TIME_ACCOUNTING && !VIRT_CPU_ACCOUNTING_NATIVE
help
Select this option to enable fine granularity task irq time
accounting. This is done by reading a timestamp on each
transitions between softirq and hardirq state, so there can be a
small performance impact.
If in doubt, say N here.
config HAVE_SCHED_AVG_IRQ
def_bool y
depends on IRQ_TIME_ACCOUNTING || PARAVIRT_TIME_ACCOUNTING
depends on SMP
config BSD_PROCESS_ACCT
bool "BSD Process Accounting"
depends on MULTIUSER
help
If you say Y here, a user level program will be able to instruct the
kernel (via a special system call) to write process accounting
information to a file: whenever a process exits, information about
that process will be appended to the file by the kernel. The
information includes things such as creation time, owning user,
command name, memory usage, controlling terminal etc. (the complete
list is in the struct acct in ). It is
up to the user level program to do useful things with this
information. This is generally a good idea, so say Y.
config BSD_PROCESS_ACCT_V3
bool "BSD Process Accounting version 3 file format"
depends on BSD_PROCESS_ACCT
default n
help
If you say Y here, the process accounting information is written
in a new file format that also logs the process IDs of each
process and its parent. Note that this file format is incompatible
with previous v0/v1/v2 file formats, so you will need updated tools
for processing it. A preliminary version of these tools is available
at .
config TASKSTATS
bool "Export task/process statistics through netlink"
depends on NET
depends on MULTIUSER
default n
help
Export selected statistics for tasks/processes through the
generic netlink interface. Unlike BSD process accounting, the
statistics are available during the lifetime of tasks/processes as
responses to commands. Like BSD accounting, they are sent to user
space on task exit.
Say N if unsure.
config TASK_DELAY_ACCT
bool "Enable per-task delay accounting"
depends on TASKSTATS
select SCHED_INFO
help
Collect information on time spent by a task waiting for system
resources like cpu, synchronous block I/O completion and swapping
in pages. Such statistics can help in setting a task's priorities
relative to other tasks for cpu, io, rss limits etc.
Say N if unsure.
config TASK_XACCT
bool "Enable extended accounting over taskstats"
depends on TASKSTATS
help
Collect extended task accounting data and send the data
to userland for processing over the taskstats interface.
Say N if unsure.
config TASK_IO_ACCOUNTING
bool "Enable per-task storage I/O accounting"
depends on TASK_XACCT
help
Collect information on the number of bytes of storage I/O which this
task has caused.
Say N if unsure.
config PSI
bool "Pressure stall information tracking"
help
Collect metrics that indicate how overcommitted the CPU, memory,
and IO capacity are in the system.
If you say Y here, the kernel will create /proc/pressure/ with the
pressure statistics files cpu, memory, and io. These will indicate
the share of walltime in which some or all tasks in the system are
delayed due to contention of the respective resource.
In kernels with cgroup support, cgroups (cgroup2 only) will
have cpu.pressure, memory.pressure, and io.pressure files,
which aggregate pressure stalls for the grouped tasks only.
For more details see Documentation/accounting/psi.rst.
Say N if unsure.
config PSI_DEFAULT_DISABLED
bool "Require boot parameter to enable pressure stall information tracking"
default n
depends on PSI
help
If set, pressure stall information tracking will be disabled
per default but can be enabled through passing psi=1 on the
kernel commandline during boot.
This feature adds some code to the task wakeup and sleep
paths of the scheduler. The overhead is too low to affect
common scheduling-intense workloads in practice (such as
webservers, memcache), but it does show up in artificial
scheduler stress tests, such as hackbench.
If you are paranoid and not sure what the kernel will be
used for, say Y.
Say N if unsure.
endmenu # "CPU/Task time and stats accounting"
config CPU_ISOLATION
bool "CPU isolation"
depends on SMP || COMPILE_TEST
default y
help
Make sure that CPUs running critical tasks are not disturbed by
any source of "noise" such as unbound workqueues, timers, kthreads...
Unbound jobs get offloaded to housekeeping CPUs. This is driven by
the "isolcpus=" boot parameter.
Say Y if unsure.
source "kernel/rcu/Kconfig"
config BUILD_BIN2C
bool
default n
config IKCONFIG
tristate "Kernel .config support"
---help---
This option enables the complete Linux kernel ".config" file
contents to be saved in the kernel. It provides documentation
of which kernel options are used in a running kernel or in an
on-disk kernel. This information can be extracted from the kernel
image file with the script scripts/extract-ikconfig and used as
input to rebuild the current kernel or to build another kernel.
It can also be extracted from a running kernel by reading
/proc/config.gz if enabled (below).
config IKCONFIG_PROC
bool "Enable access to .config through /proc/config.gz"
depends on IKCONFIG && PROC_FS
---help---
This option enables access to the kernel configuration file
through /proc/config.gz.
config IKHEADERS
tristate "Enable kernel headers through /sys/kernel/kheaders.tar.xz"
depends on SYSFS
help
This option enables access to the in-kernel headers that are generated during
the build process. These can be used to build eBPF tracing programs,
or similar programs. If you build the headers as a module, a module called
kheaders.ko is built which can be loaded on-demand to get access to headers.
config LOG_BUF_SHIFT
int "Kernel log buffer size (16 => 64KB, 17 => 128KB)"
range 12 25
default 17
depends on PRINTK
help
Select the minimal kernel log buffer size as a power of 2.
The final size is affected by LOG_CPU_MAX_BUF_SHIFT config
parameter, see below. Any higher size also might be forced
by "log_buf_len" boot parameter.
Examples:
17 => 128 KB
16 => 64 KB
15 => 32 KB
14 => 16 KB
13 => 8 KB
12 => 4 KB
config LOG_CPU_MAX_BUF_SHIFT
int "CPU kernel log buffer size contribution (13 => 8 KB, 17 => 128KB)"
depends on SMP
range 0 21
default 12 if !BASE_SMALL
default 0 if BASE_SMALL
depends on PRINTK
help
This option allows to increase the default ring buffer size
according to the number of CPUs. The value defines the contribution
of each CPU as a power of 2. The used space is typically only few
lines however it might be much more when problems are reported,
e.g. backtraces.
The increased size means that a new buffer has to be allocated and
the original static one is unused. It makes sense only on systems
with more CPUs. Therefore this value is used only when the sum of
contributions is greater than the half of the default kernel ring
buffer as defined by LOG_BUF_SHIFT. The default values are set
so that more than 64 CPUs are needed to trigger the allocation.
Also this option is ignored when "log_buf_len" kernel parameter is
used as it forces an exact (power of two) size of the ring buffer.
The number of possible CPUs is used for this computation ignoring
hotplugging making the computation optimal for the worst case
scenario while allowing a simple algorithm to be used from bootup.
Examples shift values and their meaning:
17 => 128 KB for each CPU
16 => 64 KB for each CPU
15 => 32 KB for each CPU
14 => 16 KB for each CPU
13 => 8 KB for each CPU
12 => 4 KB for each CPU
config PRINTK_SAFE_LOG_BUF_SHIFT
int "Temporary per-CPU printk log buffer size (12 => 4KB, 13 => 8KB)"
range 10 21
default 13
depends on PRINTK
help
Select the size of an alternate printk per-CPU buffer where messages
printed from usafe contexts are temporary stored. One example would
be NMI messages, another one - printk recursion. The messages are
copied to the main log buffer in a safe context to avoid a deadlock.
The value defines the size as a power of 2.
Those messages are rare and limited. The largest one is when
a backtrace is printed. It usually fits into 4KB. Select
8KB if you want to be on the safe side.
Examples:
17 => 128 KB for each CPU
16 => 64 KB for each CPU
15 => 32 KB for each CPU
14 => 16 KB for each CPU
13 => 8 KB for each CPU
12 => 4 KB for each CPU
#
# Architectures with an unreliable sched_clock() should select this:
#
config HAVE_UNSTABLE_SCHED_CLOCK
bool
config GENERIC_SCHED_CLOCK
bool
menu "Scheduler features"
config UCLAMP_TASK
bool "Enable utilization clamping for RT/FAIR tasks"
depends on CPU_FREQ_GOV_SCHEDUTIL
help
This feature enables the scheduler to track the clamped utilization
of each CPU based on RUNNABLE tasks scheduled on that CPU.
With this option, the user can specify the min and max CPU
utilization allowed for RUNNABLE tasks. The max utilization defines
the maximum frequency a task should use while the min utilization
defines the minimum frequency it should use.
Both min and max utilization clamp values are hints to the scheduler,
aiming at improving its frequency selection policy, but they do not
enforce or grant any specific bandwidth for tasks.
If in doubt, say N.
config UCLAMP_BUCKETS_COUNT
int "Number of supported utilization clamp buckets"
range 5 20
default 5
depends on UCLAMP_TASK
help
Defines the number of clamp buckets to use. The range of each bucket
will be SCHED_CAPACITY_SCALE/UCLAMP_BUCKETS_COUNT. The higher the
number of clamp buckets the finer their granularity and the higher
the precision of clamping aggregation and tracking at run-time.
For example, with the minimum configuration value we will have 5
clamp buckets tracking 20% utilization each. A 25% boosted tasks will
be refcounted in the [20..39]% bucket and will set the bucket clamp
effective value to 25%.
If a second 30% boosted task should be co-scheduled on the same CPU,
that task will be refcounted in the same bucket of the first task and
it will boost the bucket clamp effective value to 30%.
The clamp effective value of a bucket is reset to its nominal value
(20% in the example above) when there are no more tasks refcounted in
that bucket.
An additional boost/capping margin can be added to some tasks. In the
example above the 25% task will be boosted to 30% until it exits the
CPU. If that should be considered not acceptable on certain systems,
it's always possible to reduce the margin by increasing the number of
clamp buckets to trade off used memory for run-time tracking
precision.
If in doubt, use the default value.
endmenu
#
# For architectures that want to enable the support for NUMA-affine scheduler
# balancing logic:
#
config ARCH_SUPPORTS_NUMA_BALANCING
bool
#
# For architectures that prefer to flush all TLBs after a number of pages
# are unmapped instead of sending one IPI per page to flush. The architecture
# must provide guarantees on what happens if a clean TLB cache entry is
# written after the unmap. Details are in mm/rmap.c near the check for
# should_defer_flush. The architecture should also consider if the full flush
# and the refill costs are offset by the savings of sending fewer IPIs.
config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
bool
#
# For architectures that know their GCC __int128 support is sound
#
config ARCH_SUPPORTS_INT128
bool
# For architectures that (ab)use NUMA to represent different memory regions
# all cpu-local but of different latencies, such as SuperH.
#
config ARCH_WANT_NUMA_VARIABLE_LOCALITY
bool
config NUMA_BALANCING
bool "Memory placement aware NUMA scheduler"
depends on ARCH_SUPPORTS_NUMA_BALANCING
depends on !ARCH_WANT_NUMA_VARIABLE_LOCALITY
depends on SMP && NUMA && MIGRATION
help
This option adds support for automatic NUMA aware memory/task placement.
The mechanism is quite primitive and is based on migrating memory when
it has references to the node the task is running on.
This system will be inactive on UMA systems.
config NUMA_BALANCING_DEFAULT_ENABLED
bool "Automatically enable NUMA aware memory/task placement"
default y
depends on NUMA_BALANCING
help
If set, automatic NUMA balancing will be enabled if running on a NUMA
machine.
menuconfig CGROUPS
bool "Control Group support"
select KERNFS
help
This option adds support for grouping sets of processes together, for
use with process control subsystems such as Cpusets, CFS, memory
controls or device isolation.
See
- Documentation/scheduler/sched-design-CFS.rst (CFS)
- Documentation/admin-guide/cgroup-v1/ (features for grouping, isolation
and resource control)
Say N if unsure.
if CGROUPS
config PAGE_COUNTER
bool
config MEMCG
bool "Memory controller"
select PAGE_COUNTER
select EVENTFD
help
Provides control over the memory footprint of tasks in a cgroup.
config MEMCG_SWAP
bool "Swap controller"
depends on MEMCG && SWAP
help
Provides control over the swap space consumed by tasks in a cgroup.
config MEMCG_SWAP_ENABLED
bool "Swap controller enabled by default"
depends on MEMCG_SWAP
default y
help
Memory Resource Controller Swap Extension comes with its price in
a bigger memory consumption. General purpose distribution kernels
which want to enable the feature but keep it disabled by default
and let the user enable it by swapaccount=1 boot command line
parameter should have this option unselected.
For those who want to have the feature enabled by default should
select this option (if, for some reason, they need to disable it
then swapaccount=0 does the trick).
config MEMCG_KMEM
bool
depends on MEMCG && !SLOB
default y
config BLK_CGROUP
bool "IO controller"
depends on BLOCK
default n
---help---
Generic block IO controller cgroup interface. This is the common
cgroup interface which should be used by various IO controlling
policies.
Currently, CFQ IO scheduler uses it to recognize task groups and
control disk bandwidth allocation (proportional time slice allocation)
to such task groups. It is also used by bio throttling logic in
block layer to implement upper limit in IO rates on a device.
This option only enables generic Block IO controller infrastructure.
One needs to also enable actual IO controlling logic/policy. For
enabling proportional weight division of disk bandwidth in CFQ, set
CONFIG_CFQ_GROUP_IOSCHED=y; for enabling throttling policy, set
CONFIG_BLK_DEV_THROTTLING=y.
See Documentation/admin-guide/cgroup-v1/blkio-controller.rst for more information.
config CGROUP_WRITEBACK
bool
depends on MEMCG && BLK_CGROUP
default y
menuconfig CGROUP_SCHED
bool "CPU controller"
default n
help
This feature lets CPU scheduler recognize task groups and control CPU
bandwidth allocation to such task groups. It uses cgroups to group
tasks.
if CGROUP_SCHED
config FAIR_GROUP_SCHED
bool "Group scheduling for SCHED_OTHER"
depends on CGROUP_SCHED
default CGROUP_SCHED
config CFS_BANDWIDTH
bool "CPU bandwidth provisioning for FAIR_GROUP_SCHED"
depends on FAIR_GROUP_SCHED
default n
help
This option allows users to define CPU bandwidth rates (limits) for
tasks running within the fair group scheduler. Groups with no limit
set are considered to be unconstrained and will run with no
restriction.
See Documentation/scheduler/sched-bwc.rst for more information.
config RT_GROUP_SCHED
bool "Group scheduling for SCHED_RR/FIFO"
depends on CGROUP_SCHED
default n
help
This feature lets you explicitly allocate real CPU bandwidth
to task groups. If enabled, it will also make it impossible to
schedule realtime tasks for non-root users until you allocate
realtime bandwidth for them.
See Documentation/scheduler/sched-rt-group.rst for more information.
endif #CGROUP_SCHED
config UCLAMP_TASK_GROUP
bool "Utilization clamping per group of tasks"
depends on CGROUP_SCHED
depends on UCLAMP_TASK
default n
help
This feature enables the scheduler to track the clamped utilization
of each CPU based on RUNNABLE tasks currently scheduled on that CPU.
When this option is enabled, the user can specify a min and max
CPU bandwidth which is allowed for each single task in a group.
The max bandwidth allows to clamp the maximum frequency a task
can use, while the min bandwidth allows to define a minimum
frequency a task will always use.
When task group based utilization clamping is enabled, an eventually
specified task-specific clamp value is constrained by the cgroup
specified clamp value. Both minimum and maximum task clamping cannot
be bigger than the corresponding clamping defined at task group level.
If in doubt, say N.
config CGROUP_PIDS
bool "PIDs controller"
help
Provides enforcement of process number limits in the scope of a
cgroup. Any attempt to fork more processes than is allowed in the
cgroup will fail. PIDs are fundamentally a global resource because it
is fairly trivial to reach PID exhaustion before you reach even a
conservative kmemcg limit. As a result, it is possible to grind a
system to halt without being limited by other cgroup policies. The
PIDs controller is designed to stop this from happening.
It should be noted that organisational operations (such as attaching
to a cgroup hierarchy) will *not* be blocked by the PIDs controller,
since the PIDs limit only affects a process's ability to fork, not to
attach to a cgroup.
config CGROUP_RDMA
bool "RDMA controller"
help
Provides enforcement of RDMA resources defined by IB stack.
It is fairly easy for consumers to exhaust RDMA resources, which
can result into resource unavailability to other consumers.
RDMA controller is designed to stop this from happening.
Attaching processes with active RDMA resources to the cgroup
hierarchy is allowed even if can cross the hierarchy's limit.
config CGROUP_FREEZER
bool "Freezer controller"
help
Provides a way to freeze and unfreeze all tasks in a
cgroup.
This option affects the ORIGINAL cgroup interface. The cgroup2 memory
controller includes important in-kernel memory consumers per default.
If you're using cgroup2, say N.
config CGROUP_HUGETLB
bool "HugeTLB controller"
depends on HUGETLB_PAGE
select PAGE_COUNTER
default n
help
Provides a cgroup controller for HugeTLB pages.
When you enable this, you can put a per cgroup limit on HugeTLB usage.
The limit is enforced during page fault. Since HugeTLB doesn't
support page reclaim, enforcing the limit at page fault time implies
that, the application will get SIGBUS signal if it tries to access
HugeTLB pages beyond its limit. This requires the application to know
beforehand how much HugeTLB pages it would require for its use. The
control group is tracked in the third page lru pointer. This means
that we cannot use the controller with huge page less than 3 pages.
config CPUSETS
bool "Cpuset controller"
depends on SMP
help
This option will let you create and manage CPUSETs which
allow dynamically partitioning a system into sets of CPUs and
Memory Nodes and assigning tasks to run only within those sets.
This is primarily useful on large SMP or NUMA systems.
Say N if unsure.
config PROC_PID_CPUSET
bool "Include legacy /proc//cpuset file"
depends on CPUSETS
default y
config CGROUP_DEVICE
bool "Device controller"
help
Provides a cgroup controller implementing whitelists for
devices which a process in the cgroup can mknod or open.
config CGROUP_CPUACCT
bool "Simple CPU accounting controller"
help
Provides a simple controller for monitoring the
total CPU consumed by the tasks in a cgroup.
config CGROUP_PERF
bool "Perf controller"
depends on PERF_EVENTS
help
This option extends the perf per-cpu mode to restrict monitoring
to threads which belong to the cgroup specified and run on the
designated cpu.
Say N if unsure.
config CGROUP_BPF
bool "Support for eBPF programs attached to cgroups"
depends on BPF_SYSCALL
select SOCK_CGROUP_DATA
help
Allow attaching eBPF programs to a cgroup using the bpf(2)
syscall command BPF_PROG_ATTACH.
In which context these programs are accessed depends on the type
of attachment. For instance, programs that are attached using
BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
inet sockets.
config CGROUP_DEBUG
bool "Debug controller"
default n
depends on DEBUG_KERNEL
help
This option enables a simple controller that exports
debugging information about the cgroups framework. This
controller is for control cgroup debugging only. Its
interfaces are not stable.
Say N.
config SOCK_CGROUP_DATA
bool
default n
endif # CGROUPS
menuconfig NAMESPACES
bool "Namespaces support" if EXPERT
depends on MULTIUSER
default !EXPERT
help
Provides the way to make tasks work with different objects using
the same id. For example same IPC id may refer to different objects
or same user id or pid may refer to different tasks when used in
different namespaces.
if NAMESPACES
config UTS_NS
bool "UTS namespace"
default y
help
In this namespace tasks see different info provided with the
uname() system call
config IPC_NS
bool "IPC namespace"
depends on (SYSVIPC || POSIX_MQUEUE)
default y
help
In this namespace tasks work with IPC ids which correspond to
different IPC objects in different namespaces.
config USER_NS
bool "User namespace"
default n
help
This allows containers, i.e. vservers, to use user namespaces
to provide different user info for different servers.
When user namespaces are enabled in the kernel it is
recommended that the MEMCG option also be enabled and that
user-space use the memory control groups to limit the amount
of memory a memory unprivileged users can use.
If unsure, say N.
config PID_NS
bool "PID Namespaces"
default y
help
Support process id namespaces. This allows having multiple
processes with the same pid as long as they are in different
pid namespaces. This is a building block of containers.
config NET_NS
bool "Network namespace"
depends on NET
default y
help
Allow user space to create what appear to be multiple instances
of the network stack.
endif # NAMESPACES
config CHECKPOINT_RESTORE
bool "Checkpoint/restore support"
select PROC_CHILDREN
default n
help
Enables additional kernel features in a sake of checkpoint/restore.
In particular it adds auxiliary prctl codes to setup process text,
data and heap segment sizes, and a few additional /proc filesystem
entries.
If unsure, say N here.
config SCHED_AUTOGROUP
bool "Automatic process group scheduling"
select CGROUPS
select CGROUP_SCHED
select FAIR_GROUP_SCHED
help
This option optimizes the scheduler for common desktop workloads by
automatically creating and populating task groups. This separation
of workloads isolates aggressive CPU burners (like build jobs) from
desktop applications. Task group autogeneration is currently based
upon task session.
config SYSFS_DEPRECATED
bool "Enable deprecated sysfs features to support old userspace tools"
depends on SYSFS
default n
help
This option adds code that switches the layout of the "block" class
devices, to not show up in /sys/class/block/, but only in
/sys/block/.
This switch is only active when the sysfs.deprecated=1 boot option is
passed or the SYSFS_DEPRECATED_V2 option is set.
This option allows new kernels to run on old distributions and tools,
which might get confused by /sys/class/block/. Since 2007/2008 all
major distributions and tools handle this just fine.
Recent distributions and userspace tools after 2009/2010 depend on
the existence of /sys/class/block/, and will not work with this
option enabled.
Only if you are using a new kernel on an old distribution, you might
need to say Y here.
config SYSFS_DEPRECATED_V2
bool "Enable deprecated sysfs features by default"
default n
depends on SYSFS
depends on SYSFS_DEPRECATED
help
Enable deprecated sysfs by default.
See the CONFIG_SYSFS_DEPRECATED option for more details about this
option.
Only if you are using a new kernel on an old distribution, you might
need to say Y here. Even then, odds are you would not need it
enabled, you can always pass the boot option if absolutely necessary.
config RELAY
bool "Kernel->user space relay support (formerly relayfs)"
select IRQ_WORK
help
This option enables support for relay interface support in
certain file systems (such as debugfs).
It is designed to provide an efficient mechanism for tools and
facilities to relay large amounts of data from kernel space to
user space.
If unsure, say N.
config BLK_DEV_INITRD
bool "Initial RAM filesystem and RAM disk (initramfs/initrd) support"
help
The initial RAM filesystem is a ramfs which is loaded by the
boot loader (loadlin or lilo) and that is mounted as root
before the normal boot procedure. It is typically used to
load modules needed to mount the "real" root file system,
etc. See for details.
If RAM disk support (BLK_DEV_RAM) is also included, this
also enables initial RAM disk (initrd) support and adds
15 Kbytes (more on some other architectures) to the kernel size.
If unsure say Y.
if BLK_DEV_INITRD
source "usr/Kconfig"
endif
choice
prompt "Compiler optimization level"
default CC_OPTIMIZE_FOR_PERFORMANCE
config CC_OPTIMIZE_FOR_PERFORMANCE
bool "Optimize for performance (-O2)"
help
This is the default optimization level for the kernel, building
with the "-O2" compiler flag for best performance and most
helpful compile-time warnings.
config CC_OPTIMIZE_FOR_PERFORMANCE_O3
bool "Optimize more for performance (-O3)"
depends on ARC
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
Choosing this option will pass "-O3" to your compiler to optimize
the kernel yet more for performance.
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size (-Os)"
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
Choosing this option will pass "-Os" to your compiler resulting
in a smaller kernel.
endchoice
config HAVE_LD_DEAD_CODE_DATA_ELIMINATION
bool
help
This requires that the arch annotates or otherwise protects
its external entry points from being discarded. Linker scripts
must also merge .text.*, .data.*, and .bss.* correctly into
output sections. Care must be taken not to pull in unrelated
sections (e.g., '.text.init'). Typically '.' in section names
is used to distinguish them from label names / C identifiers.
config LD_DEAD_CODE_DATA_ELIMINATION
bool "Dead code and data elimination (EXPERIMENTAL)"
depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION
depends on EXPERT
depends on !(FUNCTION_TRACER && CC_IS_GCC && GCC_VERSION < 40800)
depends on $(cc-option,-ffunction-sections -fdata-sections)
depends on $(ld-option,--gc-sections)
help
Enable this if you want to do dead code and data elimination with
the linker by compiling with -ffunction-sections -fdata-sections,
and linking with --gc-sections.
This can reduce on disk and in-memory size of the kernel
code and static data, particularly for small configs and
on small systems. This has the possibility of introducing
silently broken kernel if the required annotations are not
present. This option is not well tested yet, so use at your
own risk.
config SYSCTL
bool
config HAVE_UID16
bool
config SYSCTL_EXCEPTION_TRACE
bool
help
Enable support for /proc/sys/debug/exception-trace.
config SYSCTL_ARCH_UNALIGN_NO_WARN
bool
help
Enable support for /proc/sys/kernel/ignore-unaligned-usertrap
Allows arch to define/use @no_unaligned_warning to possibly warn
about unaligned access emulation going on under the hood.
config SYSCTL_ARCH_UNALIGN_ALLOW
bool
help
Enable support for /proc/sys/kernel/unaligned-trap
Allows arches to define/use @unaligned_enabled to runtime toggle
the unaligned access emulation.
see arch/parisc/kernel/unaligned.c for reference
config HAVE_PCSPKR_PLATFORM
bool
# interpreter that classic socket filters depend on
config BPF
bool
menuconfig EXPERT
bool "Configure standard kernel features (expert users)"
# Unhide debug options, to make the on-by-default options visible
select DEBUG_KERNEL
help
This option allows certain base kernel options and settings
to be disabled or tweaked. This is for specialized
environments which can tolerate a "non-standard" kernel.
Only use this if you really know what you are doing.
config UID16
bool "Enable 16-bit UID system calls" if EXPERT
depends on HAVE_UID16 && MULTIUSER
default y
help
This enables the legacy 16-bit UID syscall wrappers.
config MULTIUSER
bool "Multiple users, groups and capabilities support" if EXPERT
default y
help
This option enables support for non-root users, groups and
capabilities.
If you say N here, all processes will run with UID 0, GID 0, and all
possible capabilities. Saying N here also compiles out support for
system calls related to UIDs, GIDs, and capabilities, such as setuid,
setgid, and capset.
If unsure, say Y here.
config SGETMASK_SYSCALL
bool "sgetmask/ssetmask syscalls support" if EXPERT
def_bool PARISC || M68K || PPC || MIPS || X86 || SPARC || MICROBLAZE || SUPERH
---help---
sys_sgetmask and sys_ssetmask are obsolete system calls
no longer supported in libc but still enabled by default in some
architectures.
If unsure, leave the default option here.
config SYSFS_SYSCALL
bool "Sysfs syscall support" if EXPERT
default y
---help---
sys_sysfs is an obsolete system call no longer supported in libc.
Note that disabling this option is more secure but might break
compatibility with some systems.
If unsure say Y here.
config SYSCTL_SYSCALL
bool "Sysctl syscall support" if EXPERT
depends on PROC_SYSCTL
default n
select SYSCTL
---help---
sys_sysctl uses binary paths that have been found challenging
to properly maintain and use. The interface in /proc/sys
using paths with ascii names is now the primary path to this
information.
Almost nothing using the binary sysctl interface so if you are
trying to save some space it is probably safe to disable this,
making your kernel marginally smaller.
If unsure say N here.
config FHANDLE
bool "open by fhandle syscalls" if EXPERT
select EXPORTFS
default y
help
If you say Y here, a user level program will be able to map
file names to handle and then later use the handle for
different file system operations. This is useful in implementing
userspace file servers, which now track files using handles instead
of names. The handle would remain the same even if file names
get renamed. Enables open_by_handle_at(2) and name_to_handle_at(2)
syscalls.
config POSIX_TIMERS
bool "Posix Clocks & timers" if EXPERT
default y
help
This includes native support for POSIX timers to the kernel.
Some embedded systems have no use for them and therefore they
can be configured out to reduce the size of the kernel image.
When this option is disabled, the following syscalls won't be
available: timer_create, timer_gettime: timer_getoverrun,
timer_settime, timer_delete, clock_adjtime, getitimer,
setitimer, alarm. Furthermore, the clock_settime, clock_gettime,
clock_getres and clock_nanosleep syscalls will be limited to
CLOCK_REALTIME, CLOCK_MONOTONIC and CLOCK_BOOTTIME only.
If unsure say y.
config PRINTK
default y
bool "Enable support for printk" if EXPERT
select IRQ_WORK
help
This option enables normal printk support. Removing it
eliminates most of the message strings from the kernel image
and makes the kernel more or less silent. As this makes it
very difficult to diagnose system problems, saying N here is
strongly discouraged.
config PRINTK_NMI
def_bool y
depends on PRINTK
depends on HAVE_NMI
config BUG
bool "BUG() support" if EXPERT
default y
help
Disabling this option eliminates support for BUG and WARN, reducing
the size of your kernel image and potentially quietly ignoring
numerous fatal conditions. You should only consider disabling this
option for embedded systems with no facilities for reporting errors.
Just say Y.
config ELF_CORE
depends on COREDUMP
default y
bool "Enable ELF core dumps" if EXPERT
help
Enable support for generating core dumps. Disabling saves about 4k.
config PCSPKR_PLATFORM
bool "Enable PC-Speaker support" if EXPERT
depends on HAVE_PCSPKR_PLATFORM
select I8253_LOCK
default y
help
This option allows to disable the internal PC-Speaker
support, saving some memory.
config BASE_FULL
default y
bool "Enable full-sized data structures for core" if EXPERT
help
Disabling this option reduces the size of miscellaneous core
kernel data structures. This saves memory on small machines,
but may reduce performance.
config FUTEX
bool "Enable futex support" if EXPERT
default y
imply RT_MUTEXES
help
Disabling this option will cause the kernel to be built without
support for "fast userspace mutexes". The resulting kernel may not
run glibc-based applications correctly.
config FUTEX_PI
bool
depends on FUTEX && RT_MUTEXES
default y
config HAVE_FUTEX_CMPXCHG
bool
depends on FUTEX
help
Architectures should select this if futex_atomic_cmpxchg_inatomic()
is implemented and always working. This removes a couple of runtime
checks.
config EPOLL
bool "Enable eventpoll support" if EXPERT
default y
help
Disabling this option will cause the kernel to be built without
support for epoll family of system calls.
config SIGNALFD
bool "Enable signalfd() system call" if EXPERT
default y
help
Enable the signalfd() system call that allows to receive signals
on a file descriptor.
If unsure, say Y.
config TIMERFD
bool "Enable timerfd() system call" if EXPERT
default y
help
Enable the timerfd() system call that allows to receive timer
events on a file descriptor.
If unsure, say Y.
config EVENTFD
bool "Enable eventfd() system call" if EXPERT
default y
help
Enable the eventfd() system call that allows to receive both
kernel notification (ie. KAIO) or userspace notifications.
If unsure, say Y.
config SHMEM
bool "Use full shmem filesystem" if EXPERT
default y
depends on MMU
help
The shmem is an internal filesystem used to manage shared memory.
It is backed by swap and manages resource limits. It is also exported
to userspace as tmpfs if TMPFS is enabled. Disabling this
option replaces shmem and tmpfs with the much simpler ramfs code,
which may be appropriate on small systems without swap.
config AIO
bool "Enable AIO support" if EXPERT
default y
help
This option enables POSIX asynchronous I/O which may by used
by some high performance threaded applications. Disabling
this option saves about 7k.
config IO_URING
bool "Enable IO uring support" if EXPERT
select ANON_INODES
default y
help
This option enables support for the io_uring interface, enabling
applications to submit and complete IO through submission and
completion rings that are shared between the kernel and application.
config ADVISE_SYSCALLS
bool "Enable madvise/fadvise syscalls" if EXPERT
default y
help
This option enables the madvise and fadvise syscalls, used by
applications to advise the kernel about their future memory or file
usage, improving performance. If building an embedded system where no
applications use these syscalls, you can disable this option to save
space.
config MEMBARRIER
bool "Enable membarrier() system call" if EXPERT
default y
help
Enable the membarrier() system call that allows issuing memory
barriers across all running threads, which can be used to distribute
the cost of user-space memory barriers asymmetrically by transforming
pairs of memory barriers into pairs consisting of membarrier() and a
compiler barrier.
If unsure, say Y.
config KALLSYMS
bool "Load all symbols for debugging/ksymoops" if EXPERT
default y
help
Say Y here to let the kernel print out symbolic crash information and
symbolic stack backtraces. This increases the size of the kernel
somewhat, as all symbols have to be loaded into the kernel image.
config KALLSYMS_ALL
bool "Include all symbols in kallsyms"
depends on DEBUG_KERNEL && KALLSYMS
help
Normally kallsyms only contains the symbols of functions for nicer
OOPS messages and backtraces (i.e., symbols from the text and inittext
sections). This is sufficient for most cases. And only in very rare
cases (e.g., when a debugger is used) all symbols are required (e.g.,
names of variables from the data sections, etc).
This option makes sure that all symbols are loaded into the kernel
image (i.e., symbols from all sections) in cost of increased kernel
size (depending on the kernel configuration, it may be 300KiB or
something like this).
Say N unless you really need all symbols.
config KALLSYMS_ABSOLUTE_PERCPU
bool
depends on KALLSYMS
default X86_64 && SMP
config KALLSYMS_BASE_RELATIVE
bool
depends on KALLSYMS
default !IA64
help
Instead of emitting them as absolute values in the native word size,
emit the symbol references in the kallsyms table as 32-bit entries,
each containing a relative value in the range [base, base + U32_MAX]
or, when KALLSYMS_ABSOLUTE_PERCPU is in effect, each containing either
an absolute value in the range [0, S32_MAX] or a relative value in the
range [base, base + S32_MAX], where base is the lowest relative symbol
address encountered in the image.
On 64-bit builds, this reduces the size of the address table by 50%,
but more importantly, it results in entries whose values are build
time constants, and no relocation pass is required at runtime to fix
up the entries based on the runtime load address of the kernel.
# end of the "standard kernel features (expert users)" menu
# syscall, maps, verifier
config BPF_SYSCALL
bool "Enable bpf() system call"
select BPF
select IRQ_WORK
default n
help
Enable the bpf() system call that allows to manipulate eBPF
programs and maps via file descriptors.
config BPF_JIT_ALWAYS_ON
bool "Permanently enable BPF JIT and remove BPF interpreter"
depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
help
Enables BPF JIT and removes BPF interpreter to avoid
speculative execution of BPF instructions by the interpreter
config USERFAULTFD
bool "Enable userfaultfd() system call"
depends on MMU
help
Enable the userfaultfd() system call that allows to intercept and
handle page faults in userland.
config ARCH_HAS_MEMBARRIER_CALLBACKS
bool
config ARCH_HAS_MEMBARRIER_SYNC_CORE
bool
config RSEQ
bool "Enable rseq() system call" if EXPERT
default y
depends on HAVE_RSEQ
select MEMBARRIER
help
Enable the restartable sequences system call. It provides a
user-space cache for the current CPU number value, which
speeds up getting the current CPU number from user-space,
as well as an ABI to speed up user-space operations on
per-CPU data.
If unsure, say Y.
config DEBUG_RSEQ
default n
bool "Enabled debugging of rseq() system call" if EXPERT
depends on RSEQ && DEBUG_KERNEL
help
Enable extra debugging checks for the rseq system call.
If unsure, say N.
config EMBEDDED
bool "Embedded system"
option allnoconfig_y
select EXPERT
help
This option should be enabled if compiling the kernel for
an embedded system so certain expert options are available
for configuration.
config HAVE_PERF_EVENTS
bool
help
See tools/perf/design.txt for details.
config PERF_USE_VMALLOC
bool
help
See tools/perf/design.txt for details
config PC104
bool "PC/104 support" if EXPERT
help
Expose PC/104 form factor device drivers and options available for
selection and configuration. Enable this option if your target
machine has a PC/104 bus.
menu "Kernel Performance Events And Counters"
config PERF_EVENTS
bool "Kernel performance events and counters"
default y if PROFILING
depends on HAVE_PERF_EVENTS
select IRQ_WORK
select SRCU
help
Enable kernel support for various performance events provided
by software and hardware.
Software events are supported either built-in or via the
use of generic tracepoints.
Most modern CPUs support performance events via performance
counter registers. These registers count the number of certain
types of hw events: such as instructions executed, cachemisses
suffered, or branches mis-predicted - without slowing down the
kernel or applications. These registers can also trigger interrupts
when a threshold number of events have passed - and can thus be
used to profile the code that runs on that CPU.
The Linux Performance Event subsystem provides an abstraction of
these software and hardware event capabilities, available via a
system call and used by the "perf" utility in tools/perf/. It
provides per task and per CPU counters, and it provides event
capabilities on top of those.
Say Y if unsure.
config DEBUG_PERF_USE_VMALLOC
default n
bool "Debug: use vmalloc to back perf mmap() buffers"
depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
select PERF_USE_VMALLOC
help
Use vmalloc memory to back perf mmap() buffers.
Mostly useful for debugging the vmalloc code on platforms
that don't require it.
Say N if unsure.
endmenu
config VM_EVENT_COUNTERS
default y
bool "Enable VM event counters for /proc/vmstat" if EXPERT
help
VM event counters are needed for event counts to be shown.
This option allows the disabling of the VM event counters
on EXPERT systems. /proc/vmstat will only show page counts
if VM event counters are disabled.
config SLUB_DEBUG
default y
bool "Enable SLUB debugging support" if EXPERT
depends on SLUB && SYSFS
help
SLUB has extensive debug support features. Disabling these can
result in significant savings in code size. This also disables
SLUB sysfs support. /sys/slab will not exist and there will be
no support for cache validation etc.
config SLUB_MEMCG_SYSFS_ON
default n
bool "Enable memcg SLUB sysfs support by default" if EXPERT
depends on SLUB && SYSFS && MEMCG
help
SLUB creates a directory under /sys/kernel/slab for each
allocation cache to host info and debug files. If memory
cgroup is enabled, each cache can have per memory cgroup
caches. SLUB can create the same sysfs directories for these
caches under /sys/kernel/slab/CACHE/cgroup but it can lead
to a very high number of debug files being created. This is
controlled by slub_memcg_sysfs boot parameter and this
config option determines the parameter's default value.
config COMPAT_BRK
bool "Disable heap randomization"
default y
help
Randomizing heap placement makes heap exploits harder, but it
also breaks ancient binaries (including anything libc5 based).
This option changes the bootup default to heap randomization
disabled, and can be overridden at runtime by setting
/proc/sys/kernel/randomize_va_space to 2.
On non-ancient distros (post-2000 ones) N is usually a safe choice.
choice
prompt "Choose SLAB allocator"
default SLUB
help
This option allows to select a slab allocator.
config SLAB
bool "SLAB"
select HAVE_HARDENED_USERCOPY_ALLOCATOR
help
The regular slab allocator that is established and known to work
well in all environments. It organizes cache hot objects in
per cpu and per node queues.
config SLUB
bool "SLUB (Unqueued Allocator)"
select HAVE_HARDENED_USERCOPY_ALLOCATOR
help
SLUB is a slab allocator that minimizes cache line usage
instead of managing queues of cached objects (SLAB approach).
Per cpu caching is realized using slabs of objects instead
of queues of objects. SLUB can use memory efficiently
and has enhanced diagnostics. SLUB is the default choice for
a slab allocator.
config SLOB
depends on EXPERT
bool "SLOB (Simple Allocator)"
help
SLOB replaces the stock allocator with a drastically simpler
allocator. SLOB is generally more space efficient but
does not perform as well on large systems.
endchoice
config SLAB_MERGE_DEFAULT
bool "Allow slab caches to be merged"
default y
help
For reduced kernel memory fragmentation, slab caches can be
merged when they share the same size and other characteristics.
This carries a risk of kernel heap overflows being able to
overwrite objects from merged caches (and more easily control
cache layout), which makes such heap attacks easier to exploit
by attackers. By keeping caches unmerged, these kinds of exploits
can usually only damage objects in the same cache. To disable
merging at runtime, "slab_nomerge" can be passed on the kernel
command line.
config SLAB_FREELIST_RANDOM
default n
depends on SLAB || SLUB
bool "SLAB freelist randomization"
help
Randomizes the freelist order used on creating new pages. This
security feature reduces the predictability of the kernel slab
allocator against heap overflows.
config SLAB_FREELIST_HARDENED
bool "Harden slab freelist metadata"
depends on SLUB
help
Many kernel heap attacks try to target slab cache metadata and
other infrastructure. This options makes minor performance
sacrifices to harden the kernel slab allocator against common
freelist exploit methods.
config SHUFFLE_PAGE_ALLOCATOR
bool "Page allocator randomization"
default SLAB_FREELIST_RANDOM && ACPI_NUMA
help
Randomization of the page allocator improves the average
utilization of a direct-mapped memory-side-cache. See section
5.2.27 Heterogeneous Memory Attribute Table (HMAT) in the ACPI
6.2a specification for an example of how a platform advertises
the presence of a memory-side-cache. There are also incidental
security benefits as it reduces the predictability of page
allocations to compliment SLAB_FREELIST_RANDOM, but the
default granularity of shuffling on the "MAX_ORDER - 1" i.e,
10th order of pages is selected based on cache utilization
benefits on x86.
While the randomization improves cache utilization it may
negatively impact workloads on platforms without a cache. For
this reason, by default, the randomization is enabled only
after runtime detection of a direct-mapped memory-side-cache.
Otherwise, the randomization may be force enabled with the
'page_alloc.shuffle' kernel command line parameter.
Say Y if unsure.
config SLUB_CPU_PARTIAL
default y
depends on SLUB && SMP
bool "SLUB per cpu partial cache"
help
Per cpu partial caches accelerate objects allocation and freeing
that is local to a processor at the price of more indeterminism
in the latency of the free. On overflow these caches will be cleared
which requires the taking of locks that may cause latency spikes.
Typically one would choose no for a realtime system.
config MMAP_ALLOW_UNINITIALIZED
bool "Allow mmapped anonymous memory to be uninitialized"
depends on EXPERT && !MMU
default n
help
Normally, and according to the Linux spec, anonymous memory obtained
from mmap() has its contents cleared before it is passed to
userspace. Enabling this config option allows you to request that
mmap() skip that if it is given an MAP_UNINITIALIZED flag, thus
providing a huge performance boost. If this option is not enabled,
then the flag will be ignored.
This is taken advantage of by uClibc's malloc(), and also by
ELF-FDPIC binfmt's brk and stack allocator.
Because of the obvious security issues, this option should only be
enabled on embedded devices where you control what is run in
userspace. Since that isn't generally a problem on no-MMU systems,
it is normally safe to say Y here.
See Documentation/nommu-mmap.txt for more information.
config SYSTEM_DATA_VERIFICATION
def_bool n
select SYSTEM_TRUSTED_KEYRING
select KEYS
select CRYPTO
select CRYPTO_RSA
select ASYMMETRIC_KEY_TYPE
select ASYMMETRIC_PUBLIC_KEY_SUBTYPE
select ASN1
select OID_REGISTRY
select X509_CERTIFICATE_PARSER
select PKCS7_MESSAGE_PARSER
help
Provide PKCS#7 message verification using the contents of the system
trusted keyring to provide public keys. This then can be used for
module verification, kexec image verification and firmware blob
verification.
config PROFILING
bool "Profiling support"
help
Say Y here to enable the extended profiling support mechanisms used
by profilers such as OProfile.
#
# Place an empty function call at each tracepoint site. Can be
# dynamically changed for a probe function.
#
config TRACEPOINTS
bool
endmenu # General setup
source "arch/Kconfig"
config RT_MUTEXES
bool
config BASE_SMALL
int
default 0 if BASE_FULL
default 1 if !BASE_FULL
config MODULE_SIG_FORMAT
def_bool n
select SYSTEM_DATA_VERIFICATION
menuconfig MODULES
bool "Enable loadable module support"
option modules
help
Kernel modules are small pieces of compiled code which can
be inserted in the running kernel, rather than being
permanently built into the kernel. You use the "modprobe"
tool to add (and sometimes remove) them. If you say Y here,
many parts of the kernel can be built as modules (by
answering M instead of Y where indicated): this is most
useful for infrequently used options which are not required
for booting. For more information, see the man pages for
modprobe, lsmod, modinfo, insmod and rmmod.
If you say Y here, you will need to run "make
modules_install" to put the modules under /lib/modules/
where modprobe can find them (you may need to be root to do
this).
If unsure, say Y.
if MODULES
config MODULE_FORCE_LOAD
bool "Forced module loading"
default n
help
Allow loading of modules without version information (ie. modprobe
--force). Forced module loading sets the 'F' (forced) taint flag and
is usually a really bad idea.
config MODULE_UNLOAD
bool "Module unloading"
help
Without this option you will not be able to unload any
modules (note that some modules may not be unloadable
anyway), which makes your kernel smaller, faster
and simpler. If unsure, say Y.
config MODULE_FORCE_UNLOAD
bool "Forced module unloading"
depends on MODULE_UNLOAD
help
This option allows you to force a module to unload, even if the
kernel believes it is unsafe: the kernel will remove the module
without waiting for anyone to stop using it (using the -f option to
rmmod). This is mainly for kernel developers and desperate users.
If unsure, say N.
config MODVERSIONS
bool "Module versioning support"
help
Usually, you have to use modules compiled with your kernel.
Saying Y here makes it sometimes possible to use modules
compiled for different kernels, by adding enough information
to the modules to (hopefully) spot any changes which would
make them incompatible with the kernel you are running. If
unsure, say N.
config ASM_MODVERSIONS
bool
default HAVE_ASM_MODVERSIONS && MODVERSIONS
help
This enables module versioning for exported symbols also from
assembly. This can be enabled only when the target architecture
supports it.
config MODULE_REL_CRCS
bool
depends on MODVERSIONS
config MODULE_SRCVERSION_ALL
bool "Source checksum for all modules"
help
Modules which contain a MODULE_VERSION get an extra "srcversion"
field inserted into their modinfo section, which contains a
sum of the source files which made it. This helps maintainers
see exactly which source was used to build a module (since
others sometimes change the module source without updating
the version). With this option, such a "srcversion" field
will be created for all modules. If unsure, say N.
config MODULE_SIG
bool "Module signature verification"
select MODULE_SIG_FORMAT
help
Check modules for valid signatures upon load: the signature
is simply appended to the module. For more information see
.
Note that this option adds the OpenSSL development packages as a
kernel build dependency so that the signing tool can use its crypto
library.
You should enable this option if you wish to use either
CONFIG_SECURITY_LOCKDOWN_LSM or lockdown functionality imposed via
another LSM - otherwise unsigned modules will be loadable regardless
of the lockdown policy.
!!!WARNING!!! If you enable this option, you MUST make sure that the
module DOES NOT get stripped after being signed. This includes the
debuginfo strip done by some packagers (such as rpmbuild) and
inclusion into an initramfs that wants the module size reduced.
config MODULE_SIG_FORCE
bool "Require modules to be validly signed"
depends on MODULE_SIG
help
Reject unsigned modules or signed modules for which we don't have a
key. Without this, such modules will simply taint the kernel.
config MODULE_SIG_ALL
bool "Automatically sign all modules"
default y
depends on MODULE_SIG
help
Sign all modules during make modules_install. Without this option,
modules must be signed manually, using the scripts/sign-file tool.
comment "Do not forget to sign required modules with scripts/sign-file"
depends on MODULE_SIG_FORCE && !MODULE_SIG_ALL
choice
prompt "Which hash algorithm should modules be signed with?"
depends on MODULE_SIG
help
This determines which sort of hashing algorithm will be used during
signature generation. This algorithm _must_ be built into the kernel
directly so that signature verification can take place. It is not
possible to load a signed module containing the algorithm to check
the signature on that module.
config MODULE_SIG_SHA1
bool "Sign modules with SHA-1"
select CRYPTO_SHA1
config MODULE_SIG_SHA224
bool "Sign modules with SHA-224"
select CRYPTO_SHA256
config MODULE_SIG_SHA256
bool "Sign modules with SHA-256"
select CRYPTO_SHA256
config MODULE_SIG_SHA384
bool "Sign modules with SHA-384"
select CRYPTO_SHA512
config MODULE_SIG_SHA512
bool "Sign modules with SHA-512"
select CRYPTO_SHA512
endchoice
config MODULE_SIG_HASH
string
depends on MODULE_SIG
default "sha1" if MODULE_SIG_SHA1
default "sha224" if MODULE_SIG_SHA224
default "sha256" if MODULE_SIG_SHA256
default "sha384" if MODULE_SIG_SHA384
default "sha512" if MODULE_SIG_SHA512
config MODULE_COMPRESS
bool "Compress modules on installation"
help
Compresses kernel modules when 'make modules_install' is run; gzip or
xz depending on "Compression algorithm" below.
module-init-tools MAY support gzip, and kmod MAY support gzip and xz.
Out-of-tree kernel modules installed using Kbuild will also be
compressed upon installation.
Note: for modules inside an initrd or initramfs, it's more efficient
to compress the whole initrd or initramfs instead.
Note: This is fully compatible with signed modules.
If in doubt, say N.
choice
prompt "Compression algorithm"
depends on MODULE_COMPRESS
default MODULE_COMPRESS_GZIP
help
This determines which sort of compression will be used during
'make modules_install'.
GZIP (default) and XZ are supported.
config MODULE_COMPRESS_GZIP
bool "GZIP"
config MODULE_COMPRESS_XZ
bool "XZ"
endchoice
config MODULE_ALLOW_MISSING_NAMESPACE_IMPORTS
bool "Allow loading of modules with missing namespace imports"
help
Symbols exported with EXPORT_SYMBOL_NS*() are considered exported in
a namespace. A module that makes use of a symbol exported with such a
namespace is required to import the namespace via MODULE_IMPORT_NS().
There is no technical reason to enforce correct namespace imports,
but it creates consistency between symbols defining namespaces and
users importing namespaces they make use of. This option relaxes this
requirement and lifts the enforcement when loading a module.
If unsure, say N.
config UNUSED_SYMBOLS
bool "Enable unused/obsolete exported symbols"
default y if X86
help
Unused but exported symbols make the kernel needlessly bigger. For
that reason most of these unused exports will soon be removed. This
option is provided temporarily to provide a transition period in case
some external kernel module needs one of these symbols anyway. If you
encounter such a case in your module, consider if you are actually
using the right API. (rationale: since nobody in the kernel is using
this in a module, there is a pretty good chance it's actually the
wrong interface to use). If you really need the symbol, please send a
mail to the linux kernel mailing list mentioning the symbol and why
you really need it, and what the merge plan to the mainline kernel for
your module is.
config TRIM_UNUSED_KSYMS
bool "Trim unused exported kernel symbols"
depends on !UNUSED_SYMBOLS
help
The kernel and some modules make many symbols available for
other modules to use via EXPORT_SYMBOL() and variants. Depending
on the set of modules being selected in your kernel configuration,
many of those exported symbols might never be used.
This option allows for unused exported symbols to be dropped from
the build. In turn, this provides the compiler more opportunities
(especially when using LTO) for optimizing the code and reducing
binary size. This might have some security advantages as well.
If unsure, or if you need to build out-of-tree modules, say N.
endif # MODULES
config MODULES_TREE_LOOKUP
def_bool y
depends on PERF_EVENTS || TRACING
config INIT_ALL_POSSIBLE
bool
help
Back when each arch used to define their own cpu_online_mask and
cpu_possible_mask, some of them chose to initialize cpu_possible_mask
with all 1s, and others with all 0s. When they were centralised,
it was better to provide this option than to break all the archs
and have several arch maintainers pursuing me down dark alleys.
source "block/Kconfig"
config PREEMPT_NOTIFIERS
bool
config PADATA
depends on SMP
bool
config ASN1
tristate
help
Build a simple ASN.1 grammar compiler that produces a bytecode output
that can be interpreted by the ASN.1 stream decoder and used to
inform it as to what tags are to be expected in a stream and what
functions to call on what tags.
source "kernel/Kconfig.locks"
config ARCH_HAS_SYNC_CORE_BEFORE_USERMODE
bool
# It may be useful for an architecture to override the definitions of the
# SYSCALL_DEFINE() and __SYSCALL_DEFINEx() macros in
# and the COMPAT_ variants in , in particular to use a
# different calling convention for syscalls. They can also override the
# macros for not-implemented syscalls in kernel/sys_ni.c and
# kernel/time/posix-stubs.c. All these overrides need to be available in
# .
config ARCH_HAS_SYSCALL_WRAPPER
def_bool n